Now showing items 1-8 of 8

    • Article

      Duration of feeding and indirect selection for growth of tilapia 

      CT Villegas & RW Doyle - Aquaculture, 1986 - Elsevier
      Duration of spontaneous feeding was observed at three times each day in a laboratory population of nine juvenile tilapia (Oreochromis mossambicus). Growth of the fish was measured as change in length and weight, and also as uptake of 14C-labelled glycine by isolated scales. Duration of the first morning feeding was highly correlated with all measures of growth and was independent of initial size. Later feedings were not correlated with growth. Selection on feeding duration could be used to select indirectly for growth rate; this might be a valuable procedure where individuals in the population are not exactly the same age (i.e., where size-at-age is an inaccurate measure of growth).
    • Article

      A farmer-oriented Nile tilapia, Oreochromis niloticus L., breed improvement in the Philippines 

      ZU Basiao, AL Arago & RW Doyle - Aquaculture Research, 2005 - Blackwell Publishing
      Opportunities for developing small-scale tilapia industry in the Philippines is hampered by the shortage of good-quality seeds and broodstock. Most small-scale farmers are dependent on distribution centres for improved tilapia seeds that are expensive and not sufficient to meet market demands. An option would be for farmers to develop their own tilapia breeds using simple procedures within their technical and financial resources. This option will also help sustain the diversity of locally adapted domestic stocks of tilapia. The Philippine tilapia production of ~ 122 316 MT can be increased by ensuring a stable supply of quality seeds and transferring suitable technology to fish farmers. The study was carried out in a tilapia hatchery/nursery pond in the Philippines to explore the potential for a farmer-based research on tilapia breed improvement using relatively simple artificial selection procedures.

      One generation of size-specific mass selection based on the early culling of large fry (collimation procedure) was applied on a Nile tilapia strain, Oreochromis niloticus L., in net cages set in a small earthen pond. Two episodes of directional selection were performed after initial removal of large fry at 21 days. Selection of parents and progeny testing were conducted in hapa and B-net cages set in earthen ponds. The selection resulted in a significant response of 8% for standard length and 29% for weight relative to the control. The crude estimates of realized heritability is ~ 16% for standard length and ~26% for weight comparable with similar studies conducted by other workers.
    • Article

      Genotype environment interaction in the response of three strains of Nile tilapia to poor nutrition 

      MRR Romana-Eguia & RW Doyle - Aquaculture, 1992 - Elsevier
      Experiments were conducted to determine the effects of poor nutrition on the growth of three Oreochromis niloticus strains fed protein-deficient diets. Four-week-old fry from the three "test" strains were paired with a fourth "reference" strain of tilapia (red) of the same size and stocked in 60-1 aquaria. The treatment lasted 6 weeks, with fish being fed commercial fish feed crumbles for the first and last 2-week periods and rice bran during weeks 3 and 4. Control fish were fed commercial diet throughout. Both control and treatment fish were fed at 20% of fish biomass per day. Lengths and weights were measured every 2 weeks.

      Significant strain effects were noted when the growth of test fish over the whole experimental period was analysed by analysis of covariance using the reference fish growth as a concomitant variable. The relative growth of the three test strains differed at each feeding phase. The NIFI strain grew best during the commercial feed phases, the Israel strain performed best during the rice bran phase while the CLSU strain, regardless of the type of nutritional environment, usually ranked last. Different performance rankings at each feeding phase represent strong genotype X environment interaction among these commercially important lines. This was statistically confirmed by analysis of covariance of the growth of the Israel and NIFI strains during the different feeding phases using the reference strain as a covariate.
    • Article

      Growth response of Nile tilapia fry to salinity stress in the presence of an ‘internal reference’ fish 

      ZU Basiao, RV Eguia & RW Doyle - Aquaculture Research, 2005 - Blackwell Publishing
      Growth of three strains of Oreochromis niloticus L. fry exposed to salinity stress in the presence of an internal reference fish were compared. The Central Luzon State University (CLSU) strain was obtained from the Freshwater Aquaculture Center, CLSU, Philippines. The ISRAEL strain was acquired from the Philippine government's Bureau of Fisheries and Aquatic Resources National Freshwater Fisheries Technology Center (BFAR-NFFTC), Munoz, Nueva Ecija. The National Inland Fisheries Institute (NIFI) strain was obtained from the NIFI, Bangkok, Thailand. Eight to nine full-sib families (replicates) per strain were split into two groups. One group was grown in freshwater for 2 weeks, acclimated to 32 ppt and reared for 2 weeks and finally grown in freshwater for another 2 weeks. Another group was contemporaneously grown in freshwater polyethylene tanks for 6 weeks. Each replicate family included a size-matched internal reference population of red tilapia strain. Two-way analysis of variance (anova) revealed no significant strain differences (P=0.081; r2=0.106). However, analysis of covariance with the internal reference strain used as a covariate showed significant (P=0.049; r2=0.638) strain effects on specific growth (based on standard length measurements). The ISRAEL strain showed consistently better growth rate in both saline and freshwater environments than the NIFI and CLSU strains. We estimated the statistical power of the two-way anova (ϕ=√(k′−1)(factor MS−s2)/(k′s>2); Zar 1984) to be ∼0.30. There was a 70% probability of a Type II error and no true difference in the growth of the three strains was detected. The use of internal reference strain as a covariate improved the r2 from 0.106 to 0.638 and increased the efficiency of the test in detecting a true difference. Other strain comparison studies in our laboratory at the Southeast Asian Fisheries Development Center Aquaculture Department showed that the ISRAEL strain shows better growth than the NIFI and CLSU strains in a crowding stress tolerance experiment, when fed only with rice bran and under restrictive feeding regimes.
    • Article

      Interaction between test and reference populations when tilapia strains are compared by the “internal control” technique 

      ZU Basiao & RW Doyle - Aquaculture, 1990 - Elsevier
      Several strains of Oreochromis niloticus, O. mossambicus and their hybrids occur in the Philippines, and others are likely to be introduced or developed locally in the near future. Our objective was to study biological interaction. The paper reports on an experimental design in which "reference" fish are included in each replicate to provide internal statistical control.

      Growth of 10 full-sib families from each of two domestic strains was compared. A third strain of red tilapia was mass spawned to provide reference fish. Thirty equal-sized fry from each family were matched with 30 red tilapia fry and reared for 8 weeks in laboratory aquaria. The fish were deliberately crowded to provide a "worst-case scenario" for the application of the reference-strain technique. The objective was to see whether behavioural interaction causes statistical or genotype × environment interactions that create problems in the analysis.

      The test strains interacted biologically with the reference strain in different ways: the growth (change in length) of strain 1 only was negatively correlated with reference growth. Statistical interaction did occur in this extreme situation. We speculate that the reference-fish technique will be more useful in experiments in ponds or cages, where variable environmental factors induce positive, rather than negative, correlations between reference and test strains.
    • Conference paper

      Is small-hold tropical aquaculture in a genetic plunge towards extinction? 

      RW Doyle - In MRR Romana-Eguia, FD Parado-Estepa, ND Salayo & MJH Lebata-Ramos (Eds.), Resource Enhancement and Sustainable Aquaculture Practices in Southeast Asia: Challenges in Responsible Production … International Workshop on Resource Enhancement and Sustainable Aquaculture Practices in Southeast Asia 2014 (RESA), 2015 - Aquaculture Department, Southeast Asian Fisheries Development Center
      Tropical shrimp aquaculture is in a disease-induced crisis of lost production. The response to this crisis currently focuses on microbiology and pathology, quarantine, and transboundary transfer of shrimp. The crisis also involves an interaction between shrimp genetics and various human interests including protection of intellectual property. Breeders of high-quality strains generally employ (and are encouraged to employ) some form of breeder lock that generates inbreeding when broodstocks are copied . Smaller hatcheries sell these copied, inbred shrimp to farmers, who thereby increase the likelihood of losing their crops to disease. The joint behavior of breeders, hatcheries and farmers causes inbreeding to accumulate in tropical regions.

      The depressive effect of inbreeding on disease resistance is exceptionally strong in shrimp, as shown in a re-analysis of published field and experimental data. Inbreeding increases the severity and frequency of disease through a variety of mechanisms. We have relatively few, marker-based estimates of accumulated inbreeding in any non-pedigreed shrimp aquaculture system. Simulation shows, however, that locked post larvae (PLs) can be distinguished from copies in broodstocks and farm ponds, given appropriate analysis of genetic markers.

      Culture of stocks certified to be free of specified pathogens (specific pathogen free or SPF stocks) is strongly recommended and only SPF stocks can now be legally imported into most jurisdictions. These recommendations are appropriate, beneficial and necessary. But insofar as they increase the commercial value of proprietary genetic strains, such regulations may also increase the likelihood of copying, and thus inbreeding at farm level and ever-increasing susceptibility to disease and climate stress (Doyle, 2014a).

      The intellectual property value of disease-resistant strains will be extremely high and intellectual property rights are fundamental to science-based economic innovation. Breeders will, and must, continue to protect their genetic improvement programs with genetic locks, especially in regions where judicial sanctions are ineffective. The regulatory objective should be to encourage biosecurity and genetic progress while discouraging copying and consequent inbreeding.

      The current consensus that inbreeding is unimportant may therefore be out of date. Inbreeding may be amplifying the severity of diseases (including the major current threats: white spot syndrome virus or WSSV, infectious hypodermal and hematopoietic necrosis virus or IHHNV and early mortality syndrome or EMS (acute hepatopancreatic necrosis disease or AHPND). Continuing to ignore the interaction between inbreeding and disease may become a fatal error for tropical shrimp aquaculture.
    • Conference paper

      A statistical procedure for using "reference fish" to compare the growth of genetic strains in aquaculture 

      RW Doyle, CA Field & Z Basiao - In R Hirano & I Hanyu (Eds.), The Second Asian Fisheries Forum. Proceedings of the Second Asian Fisheries Forum, 17-22 April 1989, Tokyo, Japan, 1990 - Asian Fisheries Society
      No simple, well-accepted procedures exist for comparing the relative performance of genetic strains of fish in aquaculture environments. The major technical problem is providing adequate statistical replication of ponds or cages. Inclusion of an "internal reference" population of standard fish in each pond can reduce replicate error caused by variation in the physical environment, food supply and population density. This statistical procedure is feasible only if there is no biological interaction (interference competition) between the strain and the reference fish. An experimental design is described in which the replicates contain different proportions of reference fish relative to the test strains. This permits the effects of interstrain interference to be estimated. Data from growth of tilapia Oreochromis mossambicus in crowded aquaria are used to illustrate the effect of interference and other nonlinearities in the experimental design.
    • Conference paper

      Use of internal reference population for growth rate comparison of tilapia strains. I. In a crowded environment 

      ZU Basiao & RW Doyle - 1990
      This paper reports an experimental design in which reference fish are included in each replicate to provide internal statistical control over environmental variation. Growth of 10 full-sib families from each of 3 strains of Oreochromis niloticus were compared in a crowded environment. A third strain of red tilapia was mass-spawned to provide reference fish. From each family, 25 equal-sized tilapia fry were matched with 25 equal-sized red tilapia fry and reared for 3 weeks in small floating cages inside a bigger tank. Growth of test strains were positively correlated with growth of the reference population. The 3 strains differed significantly in their growth rates. The reference fish technique is useful in experiments in ponds or cages, where variable environmental factors induce positive correlations between reference and test strains.